1. Field of the Invention
The present invention relates to the field of electronic system packaging. More specifically, it relates to an apparatus for mechanically stabilizing and retaining a circuit board connected to a backplane of an electronic system, e.g. a daughter card connected to a motherboard of a desktop computer.
2. Background Information
For a variety of reasons, including but not limited to interchangeability and expandability, most electronic systems, whether analog or digital, typically are modular in design. Different aspects or functions of a system are implemented on different circuit boards, thus allowing systems of varying degrees in functionality to be easily put together by including or excluding certain circuit boards. It also allows systems to be easily upgraded with additional functions by adding or replacing certain circuit boards.
Very often, one of the circuit boards is considered to be the main circuit board, against which all the other circuit boards are connected. The main circuit board is often referred to as the backplane or the motherboard, whereas the other circuit boards are often referred to as the add-on boards/cards or daughter cards. For example, in the case of personal computers, traditionally, the circuit board where the main components such as the processor and the memory are mounted is considered the motherboard. The expansion or optional functions, such as serial/parallel interfaces, game adapters, graphics and/or video adapters, network adapters, and modems, are implemented using add-on/daughter cards, which are connected to the expansion slots or connectors of the motherboard. However, in recent years, the role of the expansion slots/connectors is beginning to blur, as manufacturers begin to package processors and memory components on daughter cards.
In order for a system to operate properly, the connections between the add-on/daughter cards and the motherboard must be kept unbroken. This is generally not a problem during normal operation. However, when a system is moved or otherwise exposed to mechanical shock and vibration, the connections may become disengaged. The mechanical shock and vibration may come in any number of directions including but not limited to the direction parallel to the motherboard or the direction parallel to the add-on/daughter cards.
A number of approaches have been devised by system manufacturers to address this problem. At one end of the spectrum, the backplane/motherboard and the add-on/daughter cards are housed in a rigid mechanical structure called a card cage, which provides a frame to which daughter cards are attached by clips or screws. This is an effective but expensive solution. At the other end of the spectrum, many I/O add-on cards are retained by providing a bracket at one side edge of the circuit board, and securing the bracket against the rear frame of the system chassis. This is an inexpensive solution. However, it is not suitable for daughter cards that have high rigidity or stability requirements, or daughter cards that are "centrally" located, away from the chassis, e.g. a processor daughter card.
In between, a number of approaches are employed to provide the desired increased rigidity and stability, but without substantial increase in cost. For example, U.S. Pat. No. 5,162,979 disclosed an approach of using two pivotal levers and complementary fulcrums to secure the opposing side edges of a daughter card. The pivotal levers are mounted on opposing ends of the top edge of a daughter card, and the fulcrums are mounted on the two opposing frames of the system chassis. This is also an inexpensive solution. However, it is not suitable for daughter cards that are "centrally" located, away from the chassis, or daughter cards that do not span the entire length/width of the chassis.
Thus, it is desirable to have a circuit board retention apparatus that can offer increased rigidity and stability, but without the cost of the card cage approach, nor requiring the circuit board to span the entire length/width of the chassis. As will be described in more detail below, the circuit board retention apparatus of the present invention achieves these and other desirable results.